Separation of metal ions from aqueous solutions, such as for example Li ions, are performed by solvent extraction techniques which may be designed to be quantitative and/or selective. Such separations are accomplished by forming a readily extractable adduct of a metal ion chelate.
Lee D. A. et al. (J. Inorg. Nucl. Chem. 30, 2807-2821 (1968)) describes quantitative and selective extraction of lithium ions from aqueous metal solutions of alkali metal salts using dibenzoylmethane and trioctylphosphine oxide. Furthermore, Seeley F. G. and Baldwin W. H. (J. Inorg. Nucl. Chem. 38, 1049-1052 (1976)) report lithium extractions from near-neutral aqueous solutions of alkali metal salts, by the formation of a trioctylphosphine oxide adduct of a lithium chelate of a fluorinated beta-diketone, which was extracted into an organic diluent.
U.S. Pat. No. 3,479,147 discloses a liquid-liquid extraction method of separating lithium from other alkali metals, wherein an alkaline aqueous phase containing lithium ions was contacted with an organic solvent containing a mixture of (1) a chelating agent selected from beta-diketones and analogs thereof wherein the oxygen atoms in the beta-diketones have been replaced with nitrogen, phosphorus, or sulfur atoms, and (2) a solvating ligand such as amines and organophosphorus compounds. This mixture was reported to preferentially extract lithium ions from the aqueous phase.
Until now there has been no continuous closed loop processes in the art for the separation and removal of Li ions from aqueous liquid solutions in which purification steps have been employed, elevating the ion purity of the separated metal ion and able to regenerate the organic extracting solutions so that the method is made cost-effective in both medium and large scale production.